1. Field of the Invention
The present invention relates to an automatic lapping method for lapping a work piece including a thin film element. More particularly, it relates to an automatic lapping method for continuously lapping the work piece, as detecting a height of the thin film element, and to a lapping apparatus using the same.
For example, after forming a magnetic head thin film, the magnetic head thin film is lapped on the process of manufacturing a magnetic head. Heights of a magnetic resistance layer and a gap of the magnetic head thin film of the magnetic head are made to be constant by lapping during the manufacturing process of the magnetic head.
For the heights of the magnetic resistance layer and the gap, sub-micron order of accuracy is required. Therefore, it is necessary to lap work pieces or magnetic thin films with high accuracy.
2. Description of the Related Art
FIGS. 22A and 22B are explanatory diagrams of a composite type magnetic head.
As shown in FIG. 22A, the composite type magnetic head includes a magnetic resistance element 82 formed on a base plate 81 and a writing element 85. The magnetic resistance element 82 is formed of a magnetic resistance film 83 and a pair of conducting films 84 as shown in FIG. 22B. A resistance value of the magnetic resistance element 82 is varied by an external magnetic field. The magnetic resistance element 82 has a function to read out an electric current having a value according to magnetic field strength of a track 90 on a magnetic disk.
As the magnetic resistance element 82 is an element for reading out the current, it is required to provide a different element 85 for writing. The writing element 85 includes an inductive head. The inductive head is comprised of a lower magnetic pole 86, an upper magnetic pole 88 faced to the lower magnetic pole 86 with a certain gap, and a coil 87 provided between the lower and upper magnetic poles 86 and 88 to magnetically excite them. A non-magnetic insulating layer 89 is provided around the coil 87.
In such a composite type magnetic head, it is required to have a constant resistance value of the magnetic resistance film 83 in the magnetic resistance element 82 for each magnetic head. However, it is difficult to make the resistance value be constant or uniform on the process of manufacturing the thin film for the magnetic head. Therefore, after forming the thin film of the magnetic head, a height (width) h of the magnetic resistance film 83 is adjusted so that a resistance value may be uniformed.
FIGS. 23A, 23B, 24A, 24B, 24C and 24D are diagrams explaining the process of manufacturing the composite type magnetic head.
As shown in FIG. 23A, a plurality of composite type magnetic heads are formed on a semiconductor wafer 100 by a thin film technique. Next, as shown in FIG. 24B, the wafer 100 is cut into strips to make a plurality of row bars 101. A row bar 101 includes a plurality of the magnetic heads 102 arranged in one row. Resistance elements 102a are provided on the left and right ends, and at the center of the row bar 101 for monitoring the process of the manufacturing.
As described above, the height of the magnetic resistance film 83 for the magnetic head 102 is lapped to be constant or uniform. However, the row bar 101 is extremely thin, for example, about 0.3 mm. It is, therefore, difficult to mount the row bar 101 directly to a lapping jig, and as shown in FIG. 24C, the row bar 101 is bonded to a mounting tool or base 103 with heat dissoluble wax.
Then, as shown in FIG. 24A, the row bar 101, which is bonded to the mounting base 103, is placed on a lapping plate 104 for lapping the row bar 101. As known in Japanese Unexamined patent application published No. 2-124262 (U.S. Pat. No. 5,023,991) or Japanese Unexamined patent application published No. 5-123960, the resistance value of the resistance element 102a for monitoring is always measured while lapping the row bar 101. Then, it can be detected whether or not the magnetic resistance film of the magnetic head 102 has reached a targeted height.
When it is detected by the measurement of the resistance value that the magnetic resistance film has been lapped to the targeted height, the lapping processing is stopped. After that, a slider can be formed on a bottom surface 101-1 of the row bar 101, as shown in FIG. 24B.
The row bar 101 is further cut into a plurality of magnetic heads 102, as the row bar 101 is mounted on the mounting base 103 as shown in FIG. 24C. Each magnetic head 102 is taken out from the mounting base 103 by heating and melting the heat dissoluble wax, as shown in FIG. 24D.
In this way, a row bar 101 including a plurality of the magnetic heads 102 is prepared, and lap processing is performed for the row bar 101. Therefore, the magnetic resistance film on the plurality of magnetic heads 102 can be lapped by one step.
FIGS. 25A and 25B are explanatory diagrams of a conventional lapping apparatus.
As shown in FIG. 25A, a resistance element 102a for monitoring lapping processes, i.e., an ELG element, is formed of an analog resistance 102-1 and a digital resistance 102-2. As shown in FIG. 25B, the analog resistance 102-1 has a pattern in which the resistance value Ra becomes larger in proportion to reducing the height h of the ELG element 102a by lapping.
Therefore, it is possible to detect a height of the ELG element 102a by measuring the value of the analog resistance 102-1. That is, the relationship between the resistance value Ra and the height h of the ELG element 102a can be nearly expressed by the following equation: EQU Ra=a/h+b (1)
The height of the ELG element 102a is approximately equal to the height of the magnetic resistance film of the magnetic head 102. Therefore, it is possible to obtain the height of the magnetic resistance film by detecting the height of the ELG element 102a.
However, the relationship between the value of the analog resistance 102-1 and the height of the ELG element is varied according to the condition of the lapping processes. Therefore, a digital resistance 102-2 is provided as shown in Japanese Unexamined Patent application No. 2-124262 (U.S. Pat. No. 5,023,991).
A value Rv of the digital resistance 102-2 is varied on off positions predetermined in advance as expressed in a line graph of FIG. 25B. The off positions of the digital resistance 102-2 can be detected from the variation of the value of the digital resistance 102-2. Thereby, it becomes possible to correct the equation (1) expressing the relationship between the height of the ELG element 102a and the value of the analog resistance 102-1. That is, coefficients a and b in the relational equation (1) can be corrected.
In this way, the height of the magnetic resistance film is measured as measuring the values of the analog and digital resistances while lapping. When the height of the magnetic resistance film has reached to a target value, lapping is finished. In such the lapping method as explained above, the value of the digital resistance 102-2 is differentiated in time to detect the off positions of the digital resistance.
In such a method for measuring the resistance values in the ELG element and controlling the lapping processes, there has been some problems as follows.
At first, as shown in FIG. 25B, the varying value of the digital resistance Rv becomes small according to the reduction of the height of the ELG element. In the above explained method, it is impossible to accurately detect the off positions, because the value of the digital resistance 102-2 is differentiated in time to detect the off positions of the digital resistance. Therefore, there is a problem of lower accuracy in lapping the work piece.
Secondly, it is impossible to correctly measure resistance values because the resistance values are lowered due to influences caused by contacting the lapping plate 104 to measure the resistance values while lapping a work piece. Therefore, there has been a problem of lower accuracy in lapping the work piece.